Morphologically Cross-Shaped Ru/HZSM-5 Catalyzes Tandem Hydrogenolysis of Guaiacol to Benzene in Water

Hydrogenolysis of C−O bonds is an important tool for synthesis of valuable fuels and chemicals from biomass. In this contribution, we report that morphologically cross-shaped HZSM-5-loaded Ru nanoparticles have demonstrated high activity in the selective hydrogenolysis of guaiacol to benzene in water with 97 % yield and a rate of 7.8 g g⁻¹ h⁻¹ accompanied with high durability. N₂ sorption analysis showed that Ru/HZSM-5 (cross-shaped) had a large mesoporous surface area and pore volume for loading small and uniform Ru nanoparticles, as confirmed by TEM images. The stronger interaction of Ru and cross-shaped HZSM-5 was simultaneously confirmed by a higher hydrogen reduction temperature of RuO₂ on calcined Ru/HZSM-5, a blueshift of Ru^δ+-(CO)_n, Ru^δ+-(CO), and Ru⁰-(CO) species in the IR spectra of adsorbed CO, and a higher Ru 3d_5/2 binding energy in X-ray photoelectron spectroscopy measurements. The reaction constant in guaiacol hydrogenolysis to phenol over cross-shaped Ru/HZSM-5 (0.051 min⁻¹) was 3–4 times higher than that on spherical and cuboid Ru/HZSM-5 (0.012–0.029 min⁻¹) at identical conditions, attributed to the remarkable hydrogenolysis catalytic capability of Ru nanoparticles on cross-shaped HZSM-5. In addition, adsorption of guaiacol and hydrogen was more substantial on cross-shaped Ru/HZSM-5, as evidenced by of IR and mass spectroscopy, respectively. The higher adsorption of guaiacol is attributed to the abundant Lewis acid sites on cross-shaped Ru/HZSM-5, as the Al−OH enriched Lewis acid sites favor the adsorption of oxygen-containing guaiacol. The higher rate constant in the primary step, together with the adsorbed high concentrated reactant and hydrogen (with nearly first-order reaction kinetics) on cross-shaped Ru/HZSM-5, facilitates the overall tandem reaction, leading to an excellent hydrogenolysis catalyst working at hydrothermal conditions for biomass conversion.